Field of the Invention
The present invention relates to a photoacoustic apparatus for obtaining subject information by using a photoacoustic effect.
Description of the Related Art
In the medical field, studies are being actively carried out into optical imaging apparatuses that irradiate a subject such as a living body with light emitted from a light source such as a laser, and convert information about the subject obtained based on incident light into an image. Photoacoustic imaging (PAI) is one of optical imaging technologies. In PAI, a subject is irradiated with pulsed light generated by a light source, acoustic waves (typically, ultrasonic waves) generated from a tissue of the subject that has absorbed energy of the pulsed light propagated and diffused in the subject are received, and an image representing subject information is generated on the basis of a reception signal of the acoustic waves.
That is, with use of a difference in absorption ratio for light energy between a subject portion such as a tumor and a tissue of another portion, elastic waves (photoacoustic waves) that are generated when the subject portion absorbs emitted light energy and instantaneously expands are received by a probe. As a result of mathematically analyzing a resulting reception signal, information about the subject, in particular, an initial sound pressure distribution, a light energy absorption density distribution, an absorption coefficient distribution, or the like can be obtained. The information is also usable for quantitative measurement of a specific substance in the subject, for example, oxygen saturation in blood. In recent years, preclinical research of imaging an angiogram of a small animal by using photoacoustic imaging and clinical research of applying this principle to diagnosis of breast cancer, or the like, have been actively carried out (“Photoacoustic Tomography: In Vivo Imaging From Organelles to Organs”, Lihong V. Wang Song Hu, Science 335, 1458 (2012)).
U.S. Pat. No. 5,713,356 describes a photoacoustic apparatus that uses a probe including a plurality of transducers disposed on a hemisphere. U.S. Pat. No. 5,713,356 describes a technique of obtaining, as subject information, an initial sound pressure distribution by using a reception signal output from the probe.
In the apparatus described in U.S. Pat. No. 5,713,356, it is necessary to store reception signals output from the transducers in a memory. There is a demand for reducing the data amount of reception signals stored in the memory.